Many over the counter (o-t-c) products used to relieve deep seated pain by topical application contain irritants and relieve pain by a counterirritant action rather than by a direct analgesic effect. When such irritant containing products are applied locally to the intact skin in proper concentration to induce hyperemia and redness without blistering, they result in a feeling of warmth which may be followed by relief of pain.
Irritants have been used most successfully in treating neuralgias, rheumatoid arthritis, bursitis, myositis and integumental pain.
Capsicum is an oleoresin obtained by extracting cayenne pepper with ether. It and its active ingredient, capsaicin, have been used for many years as irritants in o-t-c compositions intended for pain relief including such well known lotions as HEET, OMEGA OIL and SLOAN'S LINIMENT. In addition, the topical analgesic cream ZOSTRIX (supplied by Gen Derm Corporation of Northbrook, Illinois) contains capsaicin 0.025% w/w in a petrolatum containing cream.
The currently available products containing capsicum or capsaicin are useful and acceptable for many purposes. However, there are applications in which it would be advantageous to have a clear, water-washable, non-greasy, capsaicin containing gel, and no such gels are currently available.